1. Technical Field
This disclosure relates to a droplet ejection device and an image forming apparatus including the droplet ejection device, and more specifically to a droplet ejection device capable of removing bubbles contained in liquid and an image forming apparatus including the droplet ejection device.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. Such image forming apparatuses may have a droplet ejection device that uses a droplet ejection head as a recording head to eject droplets of ink or other liquid.
Such a droplet-ejection type of image forming apparatus typically, while conveying a recording medium (e.g., a recording sheet of paper), ejects liquid droplets from the recording head and attaches or penetrates the droplets onto the recording medium for image formation. The recording medium (target) is not limited to the above-described recording sheet of paper but is made of string, fiber, leather, metal, resin, glass, timber, ceramic, or any other material on which liquid is attachable or penetrable.
For example, inkjet printers, one type of image forming apparatuses including such a droplet ejection device, may supply ink from an ink tank removably mounted in a printer body to a recording head on a carriage through a flexible tube. However, ink supplied through the flexible tube may contain bubbles mixed during filling of ink to the ink tank. Such bubbles may aggregate and grow up, thus causing ejection failure of liquid droplets or degraded image quality.
To prevent ink containing bubbles from being supplied to nozzles of a recording head, for example, JP-3186353-B (H07-032612-A) proposes to provide a trap portion forming a storage space in an ink supply passage to trap bubbles and a suction pump to discharge trapped bubbles to the outside.
In such a configuration, when bubbles mixed in ink supplied through the supply passage move to the trap portion by flotation, the suction pump discharges the bubbles to the outside to maintain ink in the nozzles in a bubble free state.
As one variation of the above-described configuration, for example, JP-H11-078046-A proposes an inkjet recording apparatus having an ink feed passage in an ink feed needle inserted into the ink cartridge and an introduction passage communicated with a recording head at a position offset from the ink feed passage. The inkjet recording apparatus also has a filter in an ink passage connecting the ink feed passage to the introduction passage and a bubble guide groove of a downward recessed shape formed in a ceiling face of the ink passage at an upper face side of the filter to guide and store bubbles in a bubble guide channel. As another variation of the above-described configuration, for example, JP-2004-255862-A proposes an inkjet printer having bubble discharge passages communicated with nozzles of a recording head.
In each of the above-described configurations, a bubble trap portion is formed in an ink feed (supply) passage to prevent bubbles from staying in ink supplied to a recording head.
However, for example, the configuration described in JP-3186353-B (H07-032612-A) needs not only components for ink supply but also components for bubble discharge, e.g., a suction pump, thus resulting in a relatively complex structure and increased size and cost.
Unlike the configuration of JP-3186353-B (H07-032612-A), the configuration described in JP-H11-078046-A does not have a dedicated bubble discharge means. However, it is necessary to remove bubbles accumulated in the bubble guide groove, in other words, bubbles adhered on the filter that may hamper ink supply. Hence, at initial ink filling or replacement of the ink cartridge, the inkjet recording apparatus of JP-H11-078046-A forcefully flows ink toward the ink feed passage to move bubbles from the introduction passage to the ink feed passage.
The configuration of JP-H11-078046-A is mainly intended to move bubbles away from a position of the filter opposing the introduction passage rather than to discharge bubbles to the outside. In other words, a main purpose of the configuration is to minimize bubbles adhered on the filter to secure the ink supply amount. As a result, bubbles might not be removed depending on the size of bubbles, thus blocking a portion of the ink passage proximal to the introduction passage at the restart of ink supply.
In other words, any of the above-described configurations described in JP-3186353-B (H07-032612-A) and JP-H11-078046-A supposes to move bubbles toward nozzles and does not deal with negative effect caused by bubbles moved to the nozzles.